The present invention relates to an on-screen information superimposing circuit for video signal processors, and more particularly to an on-screen information superimposing circuit in which the color signal of the on-screen information is superimposed using the color signal supplied from a video signal source.
Usually, video signal processors, which may include camcorders, video cassette recorders and so on, are composed of a recorder which records a composite video signal applied via an input onto a recording medium and a reproducer which displays a composite video signal applied via an input onto a picture display. Here, the input is in the form of a camera, a tuner circuit, or an external signal input jack connected to the output of an external system through which a composite signal is provided. Such a video signal processor has an on-screen information superimposing function to display desired on-screen information such as characters or patterns on a predetermined region of a main screen. So far, on-screen information has been formed using a luminance signal output from a video signal source (for example, a video camera) and the color signal of the on-screen information has been formed with a unicolor signal selected by a user.
In other words, in the conventional method, as shown in FIG. 1, on-screen information formed with a luminance signal supplied from a video signal source 10 is superimposed onto a main video signal to form the composite video signal. Hereinbelow, FIG. 1 is described in more detail.
As with the aforementioned input, likewise, video signal source 10 may be constructed so as to, upon input from an external system, process a video signal into a composite video signal and separate the video signal into a color signal C and a luminance signal Y. FIG. 1 assumes the video signal source 10 to be a camera. The color signal output from a video signal source 10 is applied to a first contact point S1 of a first control switch SW1 of a selector 20, and a luminance signal is applied to an A/D converter 50 as well as to a first contact point S1 of a second control switch SW2 of selector 20. A/D converter 50 converts the applied luminance signal into a digital signal and outputs it.
Here, if subject matter photographed via video signal source 10 is supposed to be used as on-screen information, a user applied a control signal to an on-screen information generator 60 via a key input 70 so that the luminance signal output from video signal source 10 is detected as the on-screen information signal.
In on-screen information generator 60, when the above control signal from key input 70 is applied to controller 61, the controller outputs a write control signal to store (or write) the digital signal output from A/D converter 50 in a memory 62. Here, memory 62 contains a readable and writable memory device. Controller 61 may be a controller only for generation of on-screen information or a microprocessor for controlling the overall function of the video signal processor. Controller 61 also controls the switching operation of selector 20. More specifically, when the information stored in memory 62 is not to be read out, in other words, when the on-screen information is not to be displayed or is not to be written on a medium, controller 61 controls selector 20 to switch first and second switches SW1 and SW2 of selector 20 to their respective first contact points S1. Thus, color signal C and luminance signal Y output directly from video signal source 10 are applied to a matrix 30. Matrix 30 is constructed to extract the R-Y and B-Y color difference signals from applied color signal C and luminance signal Y. Color signal C is composed of the three primary color signals of R, G, and B.
Meanwhile, when the information stored in memory 62 is to be read out, according to an on-screen information display control command issued by a user via a user key input, controller 61 outputs a read control signal to memory 62, a control signal for switching first and second control switches SW1 and SW2 of selector 20 to their respective second contact points S2, and a control signal to color generator 63 for outputting the color signal of the on-screen information to contact point S2 of switch SW1 of selector 20. Here, color generator 63 is constructed to have a maximum of eight colors and the color selection is carried out by the user via key input 70. Color generator 63 is capable of outputting only one of the eight colors at a time. The color consists of a pseudo-color signal. The user selects which one of the eight colors will be output.
Memory 62 outputs the stored luminance signal by the read control signal of controller 61 to a D/A converter 80. D/A converter 80 converts the applied signal to an analog signal to output it to second contact point S2 of second control switch SW2. Second control switch SW2 is switched to its second contact point S2 to send the output of D/A converter 80 to matrix 30. First control switch SW1 transmits the color signal output from color generator 63 to matrix 30. Matrix 30 outputs the two color difference signals and luminance signal according to the same operation as above, and outputs a composite video signal to a display (not shown) or to a writing medium via encoder 40. Here, when applied to the writing medium, the composite video signal passes through a written signal processor (not shown).
As described above, the conventional on-screen superimposing circuit forms on-screen information by using the luminance signal of a signal to be processed as the on-screen information among the composite video signals supplied via video signal source 10 (a camera), and superimposes the on-screen information signal on a main screen by switching selector 20. Here, due to the fact that pseudo-color signals are used, the on-screen information can be displayed using only one color. This is undesirable since a plurality of colors would produce a much more interesting and informative picture.